Bi-directional communication devices, such as cable modems, have been designed to specifically operate under a single standard, such as the North American Data Over Cable Service Interface Specifications (DOCSIS) or the European DOCSIS standards. The European version of the DOCSIS standard was not originally available when DOCSIS was first proposed to European customers. Many European cable operators started deploying the North American DOCSIS standard. These cable operators now express the need to change to a European DOCSIS-compliant system.
There are three main differences between a European DOCSIS cable modem and a North American DOCSIS cable modem. First, a diplexer within a cable modem has different cross over points, depending on whether the modem is a European DOCSIS or North American DOCSIS device, since the forward (downstream) and the return (upstream) assigned data channel bandwidths are slightly different in the two standards. This difference in the diplexer crossover point is realized by the use of different high pass filter and low pass filter cutoff frequencies in the European and North American DOCSIS compliant devices. Second, the forward data channel bandwidth is 8 MHz for a European DOCSIS compliant device, while the forward data channel bandwidth for a North American DOCSIS compliant device is 6 MHz. This difference in channel bandwidth is accomplished through the use of a different surface acoustic wave (SAW) filter to maximize performance when additional channels are located next to the desired channel without any guard band. Third, the forward data channel for European DOCSIS stipulates an alternative forward error correction (FEC) scheme than that used for North American DOCSIS. Accordingly, as cable operators change over to use of European DOCSIS-compliant cable modems, the corresponding costs rise in economies of scale to manufacture a different cable modem for each DOCSIS standard.